The present invention relates to the full-scope real-time simulation of the dynamic operation of a nuclear powered electrical generating plant secondary system for training plant operators.
The increasing demand for well trained power plant operators together with the complexity of modern day power plants, has led to the realization that the simulator is the most effective tool for such training.
Also, with advancements in nuclear power plant technology, experienced operators from time-to-time need retraining in order to be competent. An actual nuclear plant cannot provide the operator with the required experience, such as starting up, changing load, and shutting down, for example, except after years of experience; and even then, it is unlikely that he would observe the effect of important malfunctions and be able to take the best corrective procedures.
Although simulators have been used for many years, in power plant design, it is only recently that they have been used for power plant operator training. An article in the July 22, 1968 issue of "Electrical World", entitled "Nuclear Training Center Using Digital Simulation" briefly describes the installation of a boiling water reactor plant simulator. An article in the same publication in the Oct. 6, 1969 issue entitled "Huge Simulator to Ready More Reactor Operators" discusses the proposed installation of a pressurized water reactor simulator. In Volume 10, No. 5 of the publication "Nuclear Safety" published during September and October, 1969 is an article entitled "Training Nuclear Power Plant Operators With Computerized Simulators"; and in the June, 1972 issue of the publication "Power Engineering" there is an article entitled "Simulators" which describes a number of power plant operator training simulators presently in use or proposed.
Design simulators usually cover only a small part of the process, and may run slower or faster than real-time; while training simulators must operate and respond in a manner identical to the actual plant. A design simulator may involve only a narrow range of conditions, while a training simulator must simulate from cold shutdown to well beyond normal operating conditions. A design simulator usually involves only the major process, while a training simulator should cover every auxiliary system with which the plant is concerned.
Further, the full-scope simulation of a nuclear power plant for operator training is of such extensive scope that it is advantageous to provide as many modeling simplifications as possible within the limits of steady-state and transient accuracy. The mathematical modeling of a nuclear power plant is concerned with material, energy and volume balances, which often result in mathematical variables such as temperatures, pressure, material flows and flow rates, concentration of materials, specific volumes and enthalpies, mechanical speeds, vibrations, electrical current, voltage and frequency, etc.
Training simulators presently in use for operator training, which are more or less complete in their simulation utilize a digital computer that is connected to control consoles that are identical in operation and appearance to the plant being simulated. Also, an instructor's console is connected to control the simulator, introduce malfunctions, initialize the simulated plant at selected states of operation, and perform other functions useful for training purposes and control of the simulator. These computers have been of the same type used for aircraft training in some instances and process control in others.
The secondary portion of the power plant which is concerned with steam generation, turbine operation, and power output is a closed system that involves many operational situations. In order to have an accurate simulation under all conditions of operation, it should take into consideration every cause and effect that relates to actual plant operation.
For example, the reheaters that remove moisture and heat the steam after it exhausts from the high pressure turbine, should be simulated in such a way that the temperature control and safety valve for the reheater can be also simulated.
The actual plant being simulated includes a turbine electro-hydraulic controller that responds to plant operation to control steam admitting valves to the turbine. The electro-hydraulic controller should be simulated to be functionally identical regardless of the repetition rate of the computer time steps, and to correlate the controller simulation with the turbine simulation in the most economical manner.
Also, the governor valves controlled by the electro-hydraulic controller should be simulated to account for the effects of choked-flow; that is, where the pressure upstream of the valve is a predetermined amount higher than the pressure downstream of the valve.
Further, a steam turbine is subject to what is termed "windage loss", that is, a loss of shaft power, caused by the counteraction of large turbine blades against a fluid under conditions of low steam flow, for example. In order to provide a complete simulation of dynamic operation, it is desirable to simulate this windage loss.
The condenser, which in an actual plant may at times include air that is detrimental to condenser efficiency, and is symptomatic of other conditions, should be simulated so that the effect of such air is included in the dynamic calculations.
The condensate and feedwater system portion of the secondary system pumps water from the condenser hot well and the heater drain tank to the secondary side of the steam generators. Numerous valves are included that can control and divert the various flows. Condensate pumps and heater drain pumps supply the feed pumps. The feed pumps have an extremely large capacity and provide a major amount of the system's pressure increase. A non-linear solution in the simulation of a network of this type requires a solution of numerous non-linear equations which could occasionally be unstable and require an iterative technique with an uncertain solution time and perhaps nonconvergence. For real-time simulation, a method and system for simulating the feedwater system must be assured, reasonable, and predictable. For such a simulation, a linear approximation of the system permits the combining of admittances and pressure sources and permits a non-iterative simultaneous solution of the simulation equation.
The pumps in the system must be simulated over their entire operating range, which is non-linear. However, such non-linearity can be simulated by multiple linear approximation. Multiple linear approximations provide accurate representation and still allow the advantages of linear equations. The correct linear approximation can be selected during simulation execution according to pump flow and speed.
Further, the gland steam seal system that seals the shafts of the high and low pressure turbines and the generator cooling system, which cools the main generator with hydrogen, should be simulated in such a manner that they do not consume an inordinate amount of calculation time and in a simple and stable manner.